Data seem sometimes to have their own life and will, and they refuse to behave as we wish.
Then, you need a firm hand to tame the wild data and turn them into quiet and obeying pets.

Thursday, April 28, 2011

Replication : different points of view

The following quotes are the first sentences in the replication chapter of two similar books. Both are admin cookbooks. One is for PostgreSQL, one for MySQL.

Replication isn't magic, though it can be pretty cool. It's even cooler when it works, and that's what this chapter is all about.
Replication requires understanding, effort, and patience. There are a significant number of points to get right. My emphasis here is on providing simple approaches to get you started, and some clear best practices on operational robustness

Replication is an interesting feature of MySQL that can be used for a variety of purposes. It can help to balance server load across multiple machines, ease backups, provide a workaround for the lack of fulltext search capabilities in InnoDB, and much more.

The PostgreSQL quote warns of a dangerous, difficult, and unexplored path, while the MySQL one is the almost bored remark of someone whose biggest problem is to list how many good things you can do. I guess that being exposed to a given technology for longer time changes one's perception.

I received this comment from Shlomi Noach , who could not post a comment directly for technical reasons.

Hi Giuseppe,

I do a lot of original content MySQL training. What I've noticed is that I tend to take approach #1, which is to warn everyone about the possible caveats.

The outcome? I find that many times I give the wrong impression. By making sure everyone's aware of the pitfalls, I'm actually giving more weight to the cons than to the pros. Sometimes people reach the conclusion that MySQL, replication, backup & recovery, caching, etc. etc. are all things done wrong. I take note to balance this, by explicitly explaining everyone I just want them to land safe on their feet.

Psychologically (on the student's side), it's hard to both introduce something you think is useful (e.g. replication), as well as pointing out all the pitfalls.

Just for the record, I was not trying to suggest the good or bad approach to teaching replication. It just seemed funny to me that one author seemed almost afraid of touching the topic while the other considered it normal news.